Field of the Invention
The present invention relates to an annular combustion chamber of a turbine engine such as an airplane turbojet or turboprop.
Description of the Related Art
In known manner, an annular combustion chamber of a turbine engine receives a stream of air from an upstream high pressure compressor and it delivers a stream of hot gas downstream for driving rotors of high pressure and low pressure turbines.
An annular combustion chamber comprises two coaxial walls forming surfaces of revolution that extend one inside the other and that are connected together and their upstream ends by an annular chamber end wall that includes openings for mounting fuel injection systems.
Each injection system has means for supporting the head of a fuel injector and at least one swirler, which is arranged downstream from the injector head, coaxially about its axis, and which delivers a stream of air that is rotating in order to form a mixture of air and fuel that is to be burnt in the combustion chamber.
The swirlers of the injection systems are fed with air coming from an annular diffuser mounted at the outlet from the high pressure compressor that is arranged upstream from the combustion chamber.
Each swirler opens out downstream into the inside of a mixer bowl having a substantially frustoconical downstream wall that flares downstream and that is formed with an annular row of air injection orifices that are regularly distributed around the axis of the bowl.
At least one ignition spark plug is mounted in an orifice in the outer annular wall of the combustion chamber, downstream from the fuel injection systems.
In operation, the air leaving the high pressure compressor flows inside each injection system. The air/fuel mixture is ejected from each injection system and forms a substantially frustoconical rotating sheet of air and fuel that flares downstream. The flare angle of the sheet is a function of the flare angle of the frustoconical wall of the mixer bowl, and of the dimensions of the air injection orifices formed in said frustoconical wall. Thus, the larger the diameter of the orifices in the mixer bowl, the greater the flow rate of air passing each through each of these orifices and the smaller the extent to which the air/fuel mixture sheet flares. Likewise, the further upstream the holes are positioned along the frustoconical wall, the greater the aerodynamic blocking and the less the extent to which the air/fuel mixture sheet flares.
In the prior art, the injection systems of the combustion chamber produce air/fuel mixture sheets that all rotate in the same direction. The direction of rotation may equally well be clockwise or counterclockwise when looking at the injection systems from downstream.
In order to improve ignition of the air/fuel mixture sheets, it is known to arrange a spark plug on the axis of an injection system.
In its application FR 2 943 199, the Applicant proposes increasing the flare angle of the fuel sheet produced by the injection system situated closest to the spark plug. That type of configuration is found to be effective, but it can lead to the inside end of the spark plug being wetted by droplets of fuel, and that is not desirable in order to conserve optimum operation of the spark plug.